Electrolytic process



Feb. 17, 1942. J v w s HAL 2,273,795 '7 ELECTROLYTIC PROCESS Filed Dec. 31, 1936 QNVENTORS GEORGE W HEISE ERWIN A. SCHUMACHER ATTORNEY Patented Feb. 17, 1942 UNITED STATES PATENT OFFICE ELECTROLYTIC raocass George W. Heise, Rocky River, and Erwin A.

Schumacher, Lakewood, Ohio, assignors to National Carbon Company, Inc., a corporation of New York Application December a1, 1936, Serial No. 118,472

13 Claims.

(d) To provide for the removal of one or more products from the cell, in some instances in relatively concentrated form, and

(e) To increase the useful life of the electrodes.

The heart of the invention lies in the provision of an electrodehaving an effective surface area in contact with the electrolyte many times greater than the apparent or superficial area of contact, the body of the electrode being permeable either to gases alone or to both gases and liquids.

Such an electrode consists, for example, of a porous or foraminous body of conductive material, preferably carbon, the dimensions of the pores and inner passages being extremely minute, as further described below.

We are aware that it has been heretofore proposed to use carbon electrodes possessing some permeability to fluids, in various electrolytic processes in an attempt to achieve one or more of the above objects; but none of these proposals has been capable of satisfactory practical application. We have found that many of the difiiculties experienced by prior workers may be overcome by the use of an improved electrode material. Specifically, we have found that the electrode material should have a porosity above 35% (preferably between 40% and 70%, calculated as follows: porosity=100 real densityapparent iensity)-:rea1 density. Further, the electrode material should have an air permeability above 15, and preferably above 30. Whenever used herein and in the appended claims, the term air permeability" means the number of cubic inches of air per minute passing through one square inch cross-section of electrode material, when air at a pressure of one pound per square inch is blown through a block of the material one inch thick. The following table shows,

for purposes of comparison, the porosity and per- 7 meability of ordinary electrode carbons (types 1, 2, and 3) and of the special electrode carbons included in this invention (types 4, 5, 6, and 7).

Typo Porosity Percent 1 25 2 2. 28 7 3. 33 2 4. 60 2o 5. 57 3'.) 6e 4U 12" 7 42 600 We have also found that the pores of the electrode material. should be relatively minute and uniformly distributed, and not large, scattered voids and fissures. Material having the latter kind of pores might be described as leaky" rather than porous. The relative uniformity of distribution of the pores in the two kinds of materials may be distinguished by a simple test: if air is forced through a thin block of the material under water, at about the minimum air pressure required to obtain bubbles in the water, the porous" material gives forth a cloud of small bubbles over its entire surface, while the leaky material gives a number of separate streams of bubbles issuing fromthe larger fis-. sures and voids.

Another test for uniformity of porosity of these materials comprises determining the flow of a viscous liquid, such as a concentrated aqueous solution of cane sugar, under a moderate pressure, for instance a head of about six inches, through a thin (e. g. one-eighth inch) section of the material. Any relatively large fissures permit fiow of the solution and are thereby made evident.

Porous electrode material within this invention may be made from comminuted solid carbonaceous material (for example, coke, graphite, or charcoal) and a porous carbonaceous binder (for instance, baked tar or pitch). Suitable methods for making such electrode material are described in U. S. Patent 1,988,478, issued onJanuary 22,

scribed in connection with the attached drawing,

in which a Fig. 1 represents diagrammatically in vertical cross-section an electrolytic cell container l0 containing an electrolyte II in which are immersed aporous electrode 12 and a nonporous electrode I3, and a Fig. 2 represents diagrammatically in vertical cross-section an electrolytic cell similar to that shown in Fig. 1 except that it contains two porous electrodes l2 and 22.

Th device illustrated in Figure 1 may be used in cases where it is desired to introduce one or more reactants into the cell, or to remove one or more reaction products from the cell, through only one electrode.

Examples of processes in which a reactant may advantageously be introduced into the cell through a single electrode l2 involve the electrowinning of copper and zinc with the assistance of sulfur dioxide acting as an anodic depolarizer and leach-liquor regenerator.

Oxydic copper ores (or dead roasted sulfide ores of copper) may be leached with a dilute solution of sulfuric acid, yielding an acid solution containing dissolved copper sulfate. The resulting solution may be electrolyzed to yield copper at the cathode and sulfuric acid at the anode, the voltage required for electrolysis being usually between 2.1 and 2.3 volts, depending upon the anode material. It has been proposed to reduce the required voltage by introducing an anodic depolarizer, such as sulfur dioxide; but no entirely successful means for doing this has been provided. According to the present invention, depolarization may be accomplished by introducing gaseous sulfur dioxide into-the cell through a porous anode l2, as shown in Figure l. The rate of addition of sulfur dioxide is preferably so adjusted that little or no unoxidized gas remains in the electrolyte within the cell. Experiments have shown that, when the porous carbon electrode described above is used, a cell operating voltage of approximately 0.6 to 1 volt may be attained. It is necessary, of course, to prevent flooding of the electrode well I! with electrolyte in this in-' stance, and this may conveniently be accomplished by waterproofing the inner surface of the well II, using the waterproofing treatment described, for example, in our Patent 2,017,280.

Another method of introducing the sulfur dioxide into the anolyte, and this latter method enjoys several advantages over the one just described, including the advantage that the anode is not waterproofed, comprises dissolving the sulfur dioxide in a portion, or all, of the fresh, copper-containing electrolyte, introducing the resulting solution into the cell 10 through the conduit l4, and removing the exhausted electrolyte through the anode I 2 and conduit 16. Experiment has shown that this method results in a relatively low cell voltage drop of about 0.6 to 0.9 volts if a porous carbon anode is used; but has the disadvantage of permitting sulfur dioxide to escape from the surface of the electrolyte ll into the atmosphere, thereby producing unhealthy and obnoxious working conditions in the cell room.

A third method, which we prefer over those described above, comprises dissolving sulfur dioxide in a portion, or all, of the fresh, coppercontaining electrolyte; introducing the resulting solution into the cell l0 through the conduit Hi and the porous anode l2; depositing the copper at the solid cathode l3; and removing the exhausted electrolyte through a conduit IE or H. Experiment has demonstrated that free sulfur dioxide may readily be prevented from reaching the surface of the electrolyte H within the cell, and that a cell voltage drop of only about 0.6 to 0.9 volts may be attained, if a porous carbon anode is used.

Basic and oxydic ores of zinc, such as smithsonite, zincite, and calamine, or dead roasted sulfides, may be leached with a dilute sulfuric acid solution to yield an acid solution containing dissolved zinc sulfate, and this liquor may be electrolyzed to yield zinc metal, in a manner analogous to the treatment of oxydic copper ores. The voltage drop through the cell is usually about 3.3 to 3.7 volts. By the use of a porous carbon anode, and the introduction of sulfur dioxide in the first and third ways described above in connection with copper electrolysis, the voltage Under some circumstances it will be desirable to use waterproofing solutions which are considerably more concentrated than those mentioned as specific examples in this patent.

In the electrolytic process described above, the copper-containing liquor ll may be introduced into the cell l0 through a conduit M; the gaseous drop through the cell may be lowered to about 2 to 3 volts, as we have determined by experimentation.

Various attempts have been made in the past to recover copper from reduced ores by leaching with cupric chloride and subsequently electrolyzing the leach liquor. In the so-called Hoepfner process, ore leaching proceedsas follows:

Sodium chloride is added to the solution to keep the cuprous chloride in solution. Upon electrolysis, part of the copper is deposited at the cathode and part is oxidized at the anode to regenerate the leach liquor:

Deposition of the copper from a cuprous salt requires one-half the energy required to deposit it from a cupric salt. Moreover, the cuprous chloride acts as an anodic depolarizer, thereby reducing the required cell voltage. However, heretofore, difficulties with diaphragms and low current efliciencies have hindered the commercial development of the process.

We have discovered by experiment that the porous carbon electrode of this invention may be utilized to overcome the above-described difliculties. Referring to Figure l, the copper-rich leach liquor ll, containing cuprous chloride and sodium chloride, maybe introduced into a cell tion reaction maybe withdrawn through a porous carbon anode -i 2 and a suitable conduit IS. A voltage drop through the cell as low as 0.6 volt, and a current efficiency better than 90%, may be obtained.

The invention is not limited to processes involving only inorganic reactants; For instance, if the electrolyte I 1 contains a halide, such as potassium bromide, and if an unsaturated aliphatic hydrocarbon, ethylene for instance, is passed into the cell l0 through a porous carbon anode I2, aliphatic halides and halohydrins may be formed: ethylene dibromide and bromhydrin in the example ,cited.

The specific examples described above illustrate typical processes wherein we employ a porous anode and a solid cathode. It will frequently be deired, of course, to use a solid anode and a porous cathode. For instance, the latter arrange ment may be used to advantage in the cathodic reduction of nitrobenzene to p-aminophenol. In such a process, a cell l0 may be used which includes a solid anode l3 and a porous carbon cathode |2, which are immersed in a suitable electrolyte II, for instance a normal solution of sulfuric acid. Nitrobenzene may be introduced into the cell through the cathode l2, ode, the nitrobenzene is reduced cathodically to p-aminophenol which rises to the top of the electrolyte where it may be collected and removed.

Another process employing a porous cathode comprises electrolyzing sodium chloride brine in a cell l0 and passing nitric acid into the cell through a porous carbon cathode l2. Nitric acid depolarizes the cathode to form nitric oxide, and the cell reactions may be written:

Provision may be made to collect the chlorine and nitric oxide separately, and the nitric oxide may readily be oxidized and converted to nitric acid in known manner. Whereas ordinary methods of brine electrolysis require about 3.6 volts, the use of nitric acid depolarization permits operation at about 1.8 volts.

Other embodiments of our invention involve the use of a porou carbon anode and a porous I carbon cathode, as illustrated in Figure 2. For

instance, a sodium sulfate solution may be electrolyzed to produce sulfuric acid at the anode and sodium hydroxide at the cathode, according to the equation:

The sodium sulfate solution may be placed in a cell l0 through a suitable conduit l4; anolyte containing the sulfuric acid may be withdrawn through a porous carbon anode 22 and a conduit 2| and catholyte containing the caustic soda may be withdrawn through a porous carbon cathode l2; thereby eliminating the two diaphragms which would otherwise be required.

Another example of processes in which two porous carbon electrodes may be used advan- At the cathnth tageously is the electrolytic oxidation of potassium ferrocyanide to potassium ferricyanide.

In this process, the ferrocyanid solution may be I material.

unoxidized ferrocyanide may be withdrawn through a porous carbon cathode 22 provided with a well 23 and a conduit 21. The overall reaction may be represented as:

The use of two porous electrodes not only eliminates the need for diaphragms, but also provides a continuous process. A further advantage is that th ferricyanide is obtained in a concentration greater than that of the ferrocyanide. We have found by experiment that an anodic oxidation efficiency of 80% or better is obtainable.

A further example isprovided in the process wherein sulfur dioxide is passed through a porous anode into an electrolyte and chlorine is passed through a porous cathode into the electrolyte. Sulfuric acid is formed at the anode, and hydrochloric acid at the cathode. This process may be operated to deliver power, and when current from an external source is introduced the rate of output of products is increased.

Other embodiments of the invention are contemplated by us. For instance, polarization at either or both of the electrodes, which increases the resistance and opposes the flow of electric current, may be diminished by passing a fluid, which may be either a liquid or a gas, through the porous electrode into the cell or by withdrawing electrolyte from the cell through the porous electrodes, thereby mechanically decreasing the said concentration of material next to the elece trode.

In certain processes, for instance in the electrolysis of sodium chloride brine to produce chlorine at theanode, it is desired to maintain a maximum concentration of fresh electrolyte in the anolyte. By passing brine through a porous anode l2 (Figure 1) into a cell I0 containing the electrolyte II and a cathode l3, the anolyte is continually fed with fresh brine, thereby minimizing the formation of oxygen or oxygenated chlorine products and thereby also minimizing the rate and severity of the attack on the anode Furthermore, if air or oxygen is blown through the porous carbon cathode into the cell, depolarization of the cathode will reduce the power consumption of the cell; alternatively, catholyte containing the caustic soda may be .withdrawn through a porous cathode, thereby bon electrodes are characterized by a long service.

life, even in many processes wherein carbon and graphite electrodes have not been used successfully heretofore.

It will also be observed that, whenever a material is introduced into the cell through a porous electrode, the electrode serves as an efficient distributor of such material. An effect of the extended nature and chemical composition of the surface of these porous carbon electrodes which is often observed is to promote certain reactions. and one beneficial practical result is an increased efliciency of depolarization. Thus, in a given instance the porous carbon electrode may serve several functions simultaneously to achieve the genral objects of the invention.

Although several specific processes have herein been described in detail, it will readily be understood that these descriptions are presented only by way of examples illustrating certain aspects of the invention, and that the invention is not limited to or by such examples. Furthermore, although one shape of electrode is shown in the attached drawing as an example, the invention is not limited to that or any other specific shape. For instance, under some circumstances it may be desired to provide non-porous portions in the electrode, or to adopt a special shape, in order to regulate the distribution of fluid flowing through the electrode, or for another reason. It may also be advantageous to place a porous electrode or electrodes, not provided with a central well I! or 23, at the end or ends of the cell container in in such a manner that a space is left between the electrode and the container, which space may be used to serve the functions of the central well I! or 23 described herein.

We claim:

1. An electrolytic cell comprising a container; an aqueous electrolyte within the container; a porous carbon electrode and a second electrode, both of said electrodes being in contact with said electrolyte; a source of electric current connected to said electrodes; and a conduit for fluid connected to said carbon-electrode; said carbon electrode being uniformly porous and comprising solid carbon particles in a porous carbon binder having a uniform pore distribution, the porosity of said carbon electrode being between 40% and 70% and the air permeability thereof be above 30.

2. In a process of electrolyzing an aqueous trolysis, the improvement which consists in pro-,

viding as a situs for such reaction a uniformly porous carbon electrode of comminuted solid car-* bon in a uniformly porous carbon binder, the porosity of said electrode being between 35% and 70% and the air permeability thereof being above 30; and contacting said fluid reagent'with said fluid reagent with said product of electrolysis, and thereby effecting said reaction, in said situs.

3. A process of depositing metal from an aqueous electrolyte containing a salt of said metal, which comprises passing said electrolyte into a cell containing a cathode and a porous anode, said anode having a porosity between 35% and 70% and an air permeability above 30 and comprising comminuted solid carbon material em-, bedded in a porous carbon binder having uniformly distributed pores; passing an electric current through the electrolyte between the cathode and anode; and passing through the anode into the electrode a depolarizing agent.

4. A process of depositing a metal from an aqueous solution of a sulfate of said metal which comprises passing said electrolyte into a cell containing a cathodeand a porous anode, said anode having a porosity between 40% and 70% and an air permeability above 30 and comprising com- -.minuted :solid carbon material embedded in a porous carbon binder having uniformly distributed pores; passing an electric current through the electrolyte between the cathode and anode;

and passing sulfur dioxide through the mod I into the cell.

5. A process of depositing copper from an aqueous electrolyte containing cupric sulfate which comprises passing the electrolyte into a cell containing a cathode and a dry porous anode, the anode having a porosity between 35% and 70% and an air permeability above 30 and comprising comminuted solid carbon material embedded in a porous carbon binder having uniformly distributed pores; passing an electric current through the electrolyte between the cathode and anode; and passing through the anode into the electrolyte a gaseous depolarizing agent.

6. A process of depositing copper from an aqueous electrolyte containing cupric sulfate which comprises passing the electrolyte into a cell containing a cathode and a dry porous anode, the anode having a porosity between and and an air permeability above 30 and comprising comminuted solid carbon material-embedded in a porous carbon binder having uniformly distributed pores; passing an electric current through the electrolyte between the cathode and anode; and passing through the anode into the electrolyte sulfur dioxide.

7. A process of depositing copper from an aqueous electrolyte containing cupric sulfate which comprises passing the electrolyte into a cell containing a cathode and a porous anode. the anode having a porosity between 40% and 70% and an air permeability above 30 and comprising comminuted solid carbon embedded in a porous carbon binder having uniformly distributed pores; passing an electric current through the electrolyte between the cathode and anode; and passing through the anode into the electrolyte sulfur dioxide dissolved in electrolyte.

8. Method of conducting oxidation-reduction reactions which comprises passing an electrolyte into an electrolytic cell containing electrodes at least one of which is porous and has a porosity between 35% and 70% and an air permeability above 30 and comprises comminuted solid carbon material embedded in a porous carbon binder having uniformly distributed pores; passing an electric current through the electrolyte between the cathode and anode to produce oxidizing conditions at the anode and reducing conditions at the cathode; and passing material capable of entering an oxidation-reduction reaction through said porous electrode or electrodes.

9. Method of conducting organic oxidationreduction reactions which comprises passing an electrolyte into an electrolytic cell containing electrodes, at least one of which electrodes is porous and has a porosity between 40% and 70% and an air permeability above 30 and comprises comminuted solid carbon material embedded in a porous carbon binder having uniformly distributed pores; passing an electric current through the electrolyte between said electrodes to produce oxidizing conditions at the anode and reducing conditions at the cathode; and passing through said porous electrode or electrodes, into the cell, organic material capable of entering a reaction of the oxidation-reduction type.

10. Process of making organic halogen compounds which comprises'passing a solution of an electrolyzable halide into an electrolytic cell containing a cathode and a porous anode, the anode :having a.porosity between;35% and 70% and an air permeability above 30 and comprising comminuted solid carbon material embedded in a porous carbon binder having uniformly distributed pores; passing an electric current through the electrolyte between the cathode and anode, thereby electrolyzing the halide; and passing an organic material into the cell through the porous anode. 4

11. Process of making organic halogen compounds which comprises passing a solution of an electrolyzable halide into an electrolytic cell containing a cathode and a porous anode, the anode having a porosity between 40% and 70% and an air permeability above 30 and comprising comminuted solid carbon material embedded in a porous carbon binder having uniformly distributed pores; passing an electric current through the electrolyte between the cathode and anode, thereby electrolyzing the halide; and passing into the cell through the porous anode an organic material capable of reacting with halogens.

12. Process for electrolyzing halide brine which comprises passing the brine into an electrolytic cell containing an anode and a uniformly porous cathode, the cathode having a porosity above between and 70% and an air permea-bility above 15 and comprising comminuted solid carbon embedded in a porous carbon binder having uniformly distributed pores; passing an electric current through the electrolyte between the anode and cathode; and passing oxygen into the cell through the porous cathode.

13. Process for eleetrolyzing halide brine which comprises passing the brine into an electrolytic cell containing an anode and a porous cathode, the cathode having a porosity between and and an air permeability above 30 and comprising a comminuted solid carbon embedded in a porous carbon binder having uniformly distributed pores; passing an electric current through the electrolyte between the anode and cathode; and passing oxygen into the cell through the porous-cathode.

GEORGE W. I-IEISE. ERWIN A. SCHUMACHER.

CERTIFICATE OF CORRECTION. Patent No. 2,275,795; February 17, 19!;2.

' GEORGE w. BEISE, ET AL.

.It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page l, first column, lines 1 1 and b2, for "701, calculated as follows: porosity 100 real read -701) calculated as follows: i porosity 100 '(real page 11,, first column, line 52, claim 2 strike out "fluid reagent with said" page 5,

second column, line Zyclaim l2, strike out "above"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case 'in the Patent Office. Signed and sealed this 21st day of April, A. 1). 191m.-

Henry Van Arsdale, (Seal) Acting Commissioner 'of Patents. 

